Design and analysis of a soft prismatic joint by Amelia Tepper Servi.

Abstract

This thesis documents the design and analysis of a soft prismatic joint for use in soft robotics. While this joint can be utilized in any soft robot, its immediate application is for Squishbot, a soft robot developed for the DARPA Chembot challenge. For the Squishbot application, the joint must fit within a cylindrical envelope 4cm long and 1cm in diameter, compress 1.2cm axially without buckling, and be soft such that it can undergo large deformations without plastically deforming. After considering a wide range of design concepts, a screw design was chosen. This design concept was selected because it has a high axial to bending compliance ratio and does not expand radially when compressed axially. A model was developed to describe this design as a function of its design parameters. A metric was also developed to predict based on a single-cell sample whether a full-scale model would be able to fulfill the design requirements. The model was validated with respect to the parameter of blade thickness by testing 3D printed, TangoPlus cell-pairs. The results show that the model is correct to within a factor of three over blade thickness but needs further modifications to better predict trends in joint behavior. The design still needs to be tested over other parameters such as cell height. Preliminary work was also conducted on designing a locking mechanism for the joint, but more work is needed in this area. Overall, the design presented in this thesis fulfills the project's design requirements and the model that was developed describes the joint's behavior to first order.